Electrical contact and receptacle

ABSTRACT

An electrical contact is provided capable of numerous make and break electrical connections, which contact has a relatively shallow depth and is adapted to receive an elongated power blade or electrical contact to be gripped. The shallow dimension of the contact is generally normal to the longitudinal axis of the prong to receive power. The contact is preferably formed from a sheet of metal by displacing metal out of the plane of said sheet to serve as contact cams to frictionally engage the power prong. The cam makes contact with the prong end preferably after the prong end has passed through the plane of the sheet from which the contact was formed.

United States Patent [1 1 Sheldon 1 1 ELECTRICAL CONTACT AND RECEPTACLE[75] Inventor: Luther M. Sheldon, Cranston, RI.

[73] Assignee: General Electric Company,

Providence, RI.

221 Filed: June 29, 1971 21 Appl. No.: 158,072

Related US. Application Data [63] Continuation-impart of Ser. No.577,466, Sept. 6,

1966, abandoned.

[52] US. Cl. 339/59 M, 339/164 M, 339/258 P,

[51] Int. Cl HOlr 13/48 [58] Field of Search ..339/59-6l, 95, 157,

[56] References Cited UNITED STATES PATENTS 2,965,812 12/1960 Bedford,Jr. 339/18 R 7 3,212,049 10/1965 Mittler et al. 339/258 P 3,296,5761/1967 Motten, .lr 339/176 M 1 Sept. 25, 1973 1,707,702 4/1929 Alden339/277 R 2,869,093 1/1959 Benander.. 339/59 R 3,019,406 l/l962 Slater339/95 D 3,241,096 3/1966 Miller 339/157 C Primary Examiner-Joseph l-l.McGlynn Att0meyPau1 E. Rochford [57] ABSTRACT An electrical contact isprovided capable of numerous make and break electrical connections,which contact has a relatively shallow depth and is adapted to receivean elongated power blade or electrical contact to be gripped.

The shallow dimension of the contact is generally normal to thelongitudinal axis of the prong to receive power.

The contact is preferably formed from a sheet of metal by displacingmetal out of the plane of said sheet to serve as contact cams tofrictionally engage the power prong. The cam makes contact with theprong end preferably after the prong end has passed through the plane ofthe sheet from which the contact was formed.

7 Claims, 36 Drawing Figures Patented Sept. 25, 1973 '7 Sheets-Sheet 1INVENTOR. Z 11? her M. S/zeZzZon Patented Sept. 25, 1973 '7 Sheets-Sheet2 INVENTOR. lltiitfi f1. Sheldon Patented Sept. 25, 1973 7 Sheetss-Sheet15 V// //4Hlllu V W A 5/77 1/2 Z10 114 WA |H1l INVENTOR. Z 1d her [2.Sheldon Patented Sept. 25, 1973 3,761,864

7 Sheets-Sheet 4 mm M I INVENTQR. la Zher 1y. 5719142022 BY MM 6Patented Sept. 25, 1973 '7 Sheets-Sheet 5 m V M N. E14 m zm PatentedSept. 25, 1973 3,761,364

7 Sheets-Sheet 5 uvvnvrm L UTHE/P M. SHELDON BY WM 6.

Patented Sept. 25, 1973 3,761,864

7 Sheets-Sheet 7 2% VJ lNVENTOR L 1/ THE? M. SHELDON Fl G. 33

BY fwd d ATTORNE Y ELECTRICAL CONTACT AND RECEPTACLE The presentapplication is a continuation-in-part of application Ser. No. 577,466filed Sept. 6, 1966, and now abandoned, and assigned to the sameassignee as this application.

This invention relates to contact elements for electric wiring devicesand particularly to contact elements capable of requiring a higher forcefor withdrawal of a power receiving cap than for insertion of the cap.

The current carrying portions of wiring devices are conventionallyhoused or partially housed within insulating materials. Additionally,when the devices are adapted for mounting within wall receptacles theymay be provided with support or mounting members of metal and thesemembers may provide the additional feature of a grounding element.

The insulating material conventionally must provide insulatingseparation of current carrying elements. In wall mounted devices theinsulating material conventionally receives structural support mainlyfrom the metal elements of the housing. Conventionally also the plasticinsulating material furnishes structural support mainly to the currentcarrying elements.

A feature which is highly desirable in a convenience outlet to bemounted in a wall receptacle is a general thinness or small depth of thebody of plastic housing containing the metal and insulator parts of theoutlet inasmuch as the connections which supply power to the outlet arenormally made to the ends of relatively heavy gauge wire which can beextended out of a wall box by a sufficient length to permit theconnections to be made with the outlet structure of the wall. Anappreciable open volume in the wall box to receive the outlet is anadvantage in the wiring of the outlet as it accommodates multiple foldedlengths of heavy gauge wire which are pressed into the rear of the boxwhen the outlet is installed in place in the wall box.

When the wiring devices are of the portable variety as, for example,extension cords, cube taps, and the like, the yieldable insulatingmaterial may perform the function of mechanical support for the currentcarrying elements as well as providing the mechanical loadbearingcapability of the device itself.

It is deemed desirable to provide grounding contacts on portable wiringdevices but to date difficulty has been experienced in providingportable grounded devices of the multiple tap variety, i.e., a groundedconnector which can receive a plurality of grounded caps.

Further, even for the case of the connector of the more conventionalextension cord, certain performance characteristics are desirable insuch connectors but have not been available because of the excessivecost or technical difficulty of achieving these characteristics withadequate reliability and safety.

Specifically, the reliability of electrical contact is improved by adouble wipe of the current supplying electrical contact on the powerprong or blade to receive the current, i.e., a pressure contact on bothsides of the blade.

Where the power receiving element is a prong of round cross-section orregular geometric cross-section such as a square or octagon, or anarticle referred to herein generally as a blade to indicate a flattenedcrosssection as one of rectangular cross-section or the like, it ispreferred to establish contact on opposite surfaces of the prong toapply a compressive force through the cross-section configurationgenerally whether the prong is solid or hollow in cross-section.

Also, increased pressure of contact is desirable both to improvetransfer of current and to provide better mechanical holding of thepower prongs in the connector.

Further, it is desirable that the connector be capable of developinghigher holding force against withdrawal of a power prong as compared tothe force needed to insert it into the connector. Moreover, the actionof the connector contact is desirably one which provides an essentiallyreproducible holding action on the power prong, i.e., it should not besubject to being sprung or set by repeated insertion and withdrawal ofthe power prong or blade in the sense of applying substantially lowercontact pressure over an extended period of usage.

Accordingly, one object of the present invention is to provide a contactfor an electrical receptacle or connector which is simple inconstruction and yet has many of the performance characteristics ofcontacts of more complex construction.

Another object is to provide a contact in which the development ofcontact pressure is accompanied by generation of releasable tensileforces in the contact.

An additional object is to provide a connector which can require ahigher holding force against withdrawal of a power receiving cap ascompared to the force required for insertion of the cap. For thepurposes of this application a cap may be considered as a device whichprovides the terminus of a power cable or cord and which includesinsulatedly separated means for connection of a plurality of conductorsof the cable or cord to a plurality of spaced power receiving prongsadapted to receive power at different voltage levels.

Another object is to provide a convenience outlet of generally thinnercross section.

A further object of the present invention is to provide an electricalcontact having a high pressure to mass ratio, i.e., one capable ofexerting a high contact pressure against a power prong or blade relativeto the mass of material in the portion of the contact within which thecontact pressure is exerted.

Still another object of the invention is to provide an electricalconnector incorporating the novel electrical contact.

Additional objects and advantages of the present invention will be inpart apparent and in part pointed out in the description which follows.

In one of its broader aspects the objects of the present invention areachieved by providing a cammed electrical contact having at least onemetal cam adapted to exert spring pressure on an elongated element toreceive power, said cam presenting a formed face at the free end thereoffor contact with said element to develop frictional engagementtherewith,

said cam being supported at the fixed end thereof from a metal landdisposed to at least partially surround said elongated element as itapproaches contact with the free end of said cam,

said free end being adapted to follow said elongated article as it iswithdrawn from a gripped electrical contact and to undergo rotary likemotion about the fixed end thereof serving as an axis of rotation toincrease the frictional gripping pressure of said free end on saidelongated element, and

said cam being capable of deflection to limit the increase of frictionalgripping force to a value at which said elongated element may bewithdrawn.

In another of its broader aspects the objects of the present inventionare achieved by providing a land of metal to surround at least threesides of an opening adapted to receive a power blade of rectangularcross section, said land including component portions which comprise anelectrical contact structure having a generalized C form and havingspring properties, the opposed prongs of the C form being provided withgripping surfaces disposed to grip the blade under spring pressure, saidgripping surfaces being adapted to undergo a limited follower motiongenerally parallel to the motion of a gripped surface responsive to atractive force received from said gripped surface, and said C form beingcammed to increase the gripping pressure on an inserted blade responsiveto a follower motion of said gripping surfaces toward the fixed end of ablade.

In one of its narrower aspects the objects of the present invention areaccomplished by providing a land of metal capable of receivingrelatively high tensile forces within a relatively small thicknessthereof, providing within this land an opening adapted to receive agenerally rectangular power blade, said opening being defined at leastinpart by generally parallel confronting metal surfaces formed from themetal of the land and positioned to bear against the broader surfaces ofsaid blade, and being defined in an additional part by curved surfacesdisposed to be proximate and spaced from the narrowersurfaces of saidblade and disposed to distribute tensile forces developed in the metalof said land as the spacial separation of the generally parallel metalsurfaces is increased.

In another of its narrower aspects the objects of the invention areachieved by providing a connector which comprises an insulating housing,a generally planar metal member supported at its outer portions, withinsaid insulating housing, an opening in the metal member and a port inthe insulating housing communicating with said opening, said port andopening being adapted to receive an elongated power prong oflongitudinally regular cross section, said opening being formed at leastin part by displacing metal of said generally planar member out of theplane thereof to provide two essentially parallel confronting surfacesadapted to apply compressive force against the surfaces of said prong,and the non parallel portion of said opening being defined at least inpart by curved surfaces disposed to distribute tensile forces in thegenerally planar member.

In still another of its narrower aspects the objects of the inventionare achieved by providing a connector which comprises an insulatinghousing, a generally planar metal member supported at its outerportions, within said insulating housing, an opening in the metal member and a port in the insulating housing communicating with saidopening, said port and opening being adapted to receive an elongatedpower blade of generally rectangular cross section, said opening beingformed at least in part by displacing metal of said generally planarmember out of the plane thereof to provide two essentially parallelconfronting surfaces adapted to apply compressive force against thebroader surfaces of one section of said blade, and the portion of saidopening adapted to receive the narrower sur' faces of said blade beingdefined at least in part by curved surfaces disposed to distributetensile forces in the generally planar member, and said insulatinghousing bearing against outer portions of the'generally planar member tolimit deflection of portions of said member out of its generally planarconfiguration.

In the description which follows it will be evident that the contactstructure of the present invention may be provided in numerousalternative forms and an illustra tive group of such forms isspecifically described in the material that follows. However, in orderto understand the relationships between the different forms which aretaught pursuant to this invention an explanation is given here first ofa number of factors, the presence of which in several combinationstaught is of controlling importance in the operation of contactspursuant to the present invention.

l. The first factor is the form and character of the surfaces which bearagainst the blade surface and principally which permit the blade surfaceto be frictionally gripped. At least one of the surfaces must providethe electrical contact to deliver electric power to the blade. Also atleast one surface must provide a gripping action on the blade sufficientto receive tractive force from the blade as a result ofa pulling forcein the blade, i.e., one tending to withdraw the blade.

The term traction as it is used herein will be understood to mean theadhesive friction of a body on a surface against which it bears and onwhich it moves. The traction of principal concern in carrying out thisinvention is the adhesive friction of the power blade on the grippingsurface against which it bears and on which it moves.

As will be more evident from the description which follows, it is themotion of the power blade itself which gives rise to the increasedgripping force even though it is this increased gripping force whichtends to restrain withdrawal of the blade. However, the inventionresides in providing a structure which is capable of increasing thelevel of restraint by converting a part of the force applied to withdrawthe blade into a force which resists its withdrawal but does not preventthe withdrawal. Preferably the force to withdraw the blades of aconventional bladed cap is increased to a range of between 5 and 12pounds of pull to release both power blades. Accordingly the inventionprovides a need for use of increased force in withdrawing it. It doesnot reside in preventing or prohibiting the withdrawal of the blade inthe sense of locking the blade in place.

Accordingly, the gripping surface must be capable of developingincreased traction with increased pressure but must nevertheless allowthe blade to be withdrawn by a higher pulling force sufficient toovercome the higher friction resulting from the higher pressure. As usedin the application the term tractive force indicates the force deliveredto the gripping surface from the blade due to a withdrawal force appliedto the blade. As the pressure of the gripping surface on the blade isincreased, the tractive force received by the gripping surface can beincreased due to the higher traction between the surfaces at the higherpressure.

The term friction is used to indicate the force needed to overcome theresistance to slippage, or in other words the resistance to movement ofthe blade surface relative to the gripping surface generally parallel tothe plane of their contact.

What is required pursuant to this invention is a friction grip in thesense that increased pressure of the gripping surface on that bladeresults in increased friction but does not result in significantindentation or deformation of the blade.

Where the gripping surface is at the end of a metal cam, the grippingsurface must not have a form which will lock the power blade in place inthe manner for example in which the locking tongue of the cams of US.Pat. No. 2,705,785 lock a wire in place. Rather the gripping surface ofa cam must be one which will yield to a higher withdrawal force to allowmovement of the power blade in frictional contact with the grippingsurface of the cam, even though the frictional contact is at the higherfriction level induced by the higher pressing force generated betweenthe gripping surface of the cam and blade by a cam action explained morefully below. It is for this reason, i.e., to distinguish from a lockingaction that the surface and cam are referred to herein as a grippingsurface or gripping cam rather than as a locking surface or locking cam.

In a preferred form of the present invention a gripping surface isformed at or near the end of a gripping cam by so forming the end of thecam as to permit withdrawal of the blade under the higher pressureinduced by the cam action. The forming of the cam end may be the resultof the bending or folding of the cam end on which the gripping surfaceis formed. When the cam is formed from a metal strip as by stamping thegripping surface may be the result of a secondary forming action on theend section of metal as by peening or coining or the like to round itand eliminate the sharp edge normally produced by shearing of the stripto establish cam edges. It may be formed by extending the cam edges asby a cupping-like extension of the cam surfaces before the shear of theaffected section of the strip occurs and the folding back or bending ofthe extended cams at the end of the cupping-like stroke.

In another preferred embodiment of the invention described more fullybelow the sheared surface may be bent out of the expected path of thepower blade and the portion of the cam proximate but not immediately atthe cam end may be used as the gripping surface. When this is done it ispreferred to bend the sheared edge through more than 90 in order topreclude its presenting its sharp edge to the blade or to anyirregularity of the blade as the blade is withdrawn as this can resultin a locking type of cam action.

It is important to understand that the contacting and gripping actionsprovided in accordance with the present invention are suitable for use alarge number of times and over a long period of time without significantchange to the surface of a conventional smooth surfaced power bladecontacted and gripped.

II. A second factor is the presence of a minimum electrical contactpressure. This factor is essential because when the blade is firstinserted there must be sufficient force tending to press the bladeagainst the electrical contact to ensure that electrical contact will beestablished and maintained. Further although changes in grippingstrength may be induced pursuant to this invention these changes,whether increases or reductions in gripping strength, must not interferewith or interrupt adequate electrical contact pressure on which supplyof electric power to the power blade depends.

A preferred mode for producing and ensuring a continuation of a minimumcontact pressure is through use of spring pressure between the contactsurface supplying electric power and the blade.

Further the initial friction of the gripping surface on the bladesurface is preferably provided by a spring pressure sufficient to causethe gripping surface to be so frictionally engaged as to serve asafollower to the blade surface serving as a driver and to receivetractive force from the blade surface and to follow motion of the bladegenerally parallel to its longitudinal axis.

Ill. A third factor is that of the relative freedom of the grippingsurface in contact with the surface of the power blade to move generallyparallel to the direction of movement of the power blade as the powerblade is pulled so as to withdraw it. This gripping surface shouldgenerally be sufficiently free to undergo this movement so that thefrictional contact of the cam against the blade surface due to theavailable spring or other residual pressure between the contacting camsurface and the blade surface will be sufficient to provide a minimumtractive force and to initiate this movement. Based on the movement ofthe gripping surface responsive to this tractive force the grippingpressure may be increased to a pressure level above that due to thespring alone.

IV. The fourth factor is the capability of the body supporting thegripping surface to generate an increased gripping force as a result ofthe follower motion imparted to the gripping surface. Essentially thisis a capacity of the member supporting the gripping surface to translatea tractive force transmitted from the blade to the supporting memberinto increased pressure of the gripping surface on the blade surface.

In the description which follows this will be described in terms of acam action. While the third factor is essentially symmetrical in itsaction the cam action is principally asymmetric in that it amounts to anincrease of force received from or taken from blade during bladewithdrawal relative to that taken during insertion.

The cam action of the present invention, stated in a somewhatoversimplified fashion, involves a cam being turned through anessentially rotary movement as a result of an essentially linearmovement of the contacting surface of the contacting cam end for adistance and in a direction generally parallel to the surface of theblade being withdrawn. Pursuant to this somewhat oversimplified viewboth the power blade and the cam are viewed as each having a fixed endand a free end. The fixed end of the cam is more remote from the planeof the contacted blade surface than the free end of the cam. Further,the fixed cam end is disposed on the side of an imaginary plane normalto the longitudinal axis of the power blade and intersecting the pointwhere the blade surface is contacted by the fixed cam end which isclosest to the fixed end of the power blade.

Accordingly a line extending from the free end of the cam to the fixedend of the cam will describe an acute angle with reference to both oftwo planes which intersect at The first is the plane of the bladesurface contacted and the second is the plane normal to the longitudinalaxis of the blade and passing through the blade surface at the point ofcontact of the free end of the cam with the blade surface. If the camand blade start in this spacial relation, the contacting surface of thefree end of the cam essentially follows the contacted portion of thesurface of the power blade. This generally linear following movement ofthe free cam end results in a tendency toward an at least partial rotarymovement of the cam about its fixed end, i.e., a tendency to increasethe acute angle between the line Joining the free and fixed ends of thecam and the plane of the blade surface.

If we depart from the oversimplified view it will be evident that thevalues of parameters on which the cam action described above depends maybe changed. For example, the cam may itself undergo a deflectionparticularly when it is formed of a strip or part of a strip of springmetal and as a result one of more of several parameters maysimultaneously or sequentially change as follows:

A. The point of contact of the free cam end with the blade surface canbe changed;

B. The length of line between the contacting surface at the free end andthe fixed end may be shortened; and

C. The location of the fixed end as indicated by the point about whichthe cam tends to be rotated, may be moved.

However, if the described essential relationships are present, namelythe initial spring pressure of the cam against the blade surface,freedom of the free cam end to follow the blade, based on frictiongenerated by the spring pressure, and the enlargement of the acute angledescribed by the blade surface and the line joining the fixed end of thecam with the point of contact of the cam with the blade surface, it willalso be evident that the cam action to increase pressure of the free endof the cam against the blade surface in accordance with the presentinvention will occur.

V. The fifth factor in the operation of the increased pressure contactof the present invention is the control and limitation of the rate ofincrease of the increased gripping force. This factor includes controlof the angle at which the cams are disposed to the blade surfaces whichthey contact under conventional spring pressure, and the provision ofany boss or stop to limit the extent of movement of the cam. This may beexplained more clearly by reference first to conventional fingeredcontact operation.

For the conventional spring pressure contact of a conventional fingeredcontact, the general longitudinal axis of the spring loaded fingers aredisposed generally parallel to the longitudinal axis of the blade. Whenthis is the case, essentially all pressure between the blade and thecontacts will be the result of the spring force applied through thespring action which is generated when the contact fingers are separatedby the wedging force of the entering power blade.

The difference between the conventional generation of contact pressureand that generated pursuant to the present invention is evident from theobservation that in the use of the conventional fingered contact thegreatest force is normally needed to separate the fingers against acombined spring force in the fingers being separated, and a frictionalforce at the finger surfaces. Both forces are applied to resist thespreading of the fingers by the tip of the entering blade, and normallyconstitute the highest force used in using the contact. The frictionalforce between parallel surfaces of a fully inserted blade and thecontacted surfaces of the fingers, as withdrawal of the blade isstarted, is usually not increased because the frictional force dependson the level of spring force applied through the fingers and this doesnot increase as parallel smooth surfaces of a power blade are withdrawn.An increase in the spring force of the fingers as withdrawal occurscannot normally generate a wider separation of the fingers on which anincrease of spring pressure must normally depend.

By contrast and pursuant to the present invention contact or grippingpressure may be increased within a wide range of increments byestablishing spring pressure on the blade as an initial force whichresists withdrawal of the blade, and by using the outward movement ofthe blade to impart motion to the contact, and further by employing thismotion of the contact to increase the pressure acting on the bladesurface to a level above that applied by the initial spring pressurealone.

The amount of increase of the contact pressure is subject to controlwithin a wide range by adjustment of the angle at which the cams aredisposed to the blade when the withdrawal of the blade initiates arotation or deflection of the cams such as is responsible for increasingcontact pressure on the blade. For example if the cams are set at anangle slightly less than with respect to the blade surface and are freeto turn as indicated in 1 above, then as the power blade is withdrawn anenormous increase in pressure between the blade and the cam will occurbecause of the very high mechanical advantage at work as the cam isrotated through the small angle which multiplies and magnifies itspressing power. This enormous increase can be offset in part byemploying cams which themselves are subject to spring deflection as thiscan allow the cams to deflect and thus limit the actual pressure appliedto the blade that inherent in the spring qualities of the cam.

Except for a limiting mechanism to limit the actual pressure applied tothe cams as described above, if more than half of an increased pullingforce is converted to increased gripping force the net effect ofincreasing the pull can be to so magnify the gripping force as to tendto lock the blade in the grip of the device. However, pursuant to oneembodiment of this invention the locking result is avoided by limitingthe level of increase of pull to between 50 and 300 percent of aninitial level and by limiting the initial level to 7 pounds and theupper level to 12 pounds.

VI. The sixth and last factor is the provision of a means to contain theincreased compressive forces generated in the blade due to the increasedgripping pressure generated by the cam action of the contact of thepresent invention. This is preferably accomplished in the internallycammed contacts described below by providing a land of metal, and bydisposing the cams relative to the land so that they generatecompressive forces in the metal of the land where the cams are affixedand opposed tensile forces in the land metal portions which join theportions under compression. it is this ability of the land to absorb thecombination of increased tensile and compressive forces without bucklingor being deformed or broken which is the essence of the sixth orpressure containment factor.

In the externally cammed contact also described below the tensile forceis contained partly in the metal land proximate the blade edges andpartly in an insulating cover of the device against which the fixed endsof the cams bear.

For blades of rectangular cross section the increased gripping pressureof the contact structures of the present invention are at leastpartially offset, balanced or contained by increased tensile forces inthe material proximate the blade edges and closer to the fixed end ofthe blade than the portion of the blade at which the increased grippingforce is applied.

While the foregoing explanation of the combination of principles ofoperation of cams and cam contacts operating in accordance with thecombination of requirements and features of this invention is givenprincipally with reference to contacting of power blades it will beevident particularly from consideration of the cams and contacts ofFIGS. 28 through 36 that the combination of principles of the presentinvention may be applied as well to power prongs of cross section otherthan the rectangular cross section referred to generally herein as powerblades.

The concepts of the present invention and the manner in which they maybe most advantageously embodied in wiring devices may be explained mostclearly by reference to the following drawings in which:

FIG. 1 is a perspective view in part in section of a connector formedprusuant to the present invention to contain a contact as providedpursuant to the invention;

FIG. 2 is a section of FIG. 1 taken along 2-2 of FIG. 1 and showing acap mounted in place in the connector;

FIG. 3 is a plan view of a contact strip at one stage of its formation;

FIG. 4 is a similar view of the strip after formation has beencompleted;

FIG. 5 is an elevational view of the contact of FIG. 4 a portion of theright end of which is broken away;

FIG. 6 is a vertical section of the contact of FIG. 5 taken along theline 6-6 of FIG. 5;

FIG. 7 is a perspective view of a detail of a contact such as that shownin FIG. 4 emphasizing certain constructional details of the contactstrip and the relation of the contact to power blades to be brought intoelectrical contact with the contact structure;

FIG. 8 is a sectional view of a detail of the contact strip of FIG. 3taken along the line 88 of FIG. 3;

FIG. 9 is a detail ofa first step in the formation of the strip as shownin FIG. 4;

FIG. 10 is a similar detailed view of a section of the completed stripas shown in FIG. 4;

FIG. 11 is a transverse sectional view of the strip of FIG. 16 takenalong the line ll-l1 of FIG. 16 showing the first stage of formation ofan externally cammed contact;

FIG. 12 is a similar detailed sectional view of the strip after a firststep of formation has been completed;

FIG. 13 is a similar detailed view of the strip after a second formationstep has been completed;

FIG. 14 is a detailed sectional view of a later step in the formation ofa completed contact;

FIG. 15 is a detailed sectional view of the contact essentially in itscompletely formed condition;

FIG. 16 is a top plan view of the contact at a first stage of itspreparation as also illustrated in FIG. 11;

FIG. 17 is a top plan view of the contact after formation has beencompleted as illustrated also in FIG. 15;

FIG. I8 is a perspective view of a contact strip for a rigid walledoutlet which incorporates a contact element such as are shown in FIGS.15 and 17 as the blade receiving elements;

FIG. 19 is a vertical transverse section of a conventional rigid walledoutlet showing the relationship 'between the contact of FIG. 18 and therigid walled insulating housing of the outlet;

FIG. 20 is a perspective view ofa contact adapted to receive powerblades at either of two alignments essentially at right angles;

FIG. 21 illustrates the contact of FIG. 20 with a first blade in place;and

FIG. 22 illustrates the contact of FIG. 20 with the alternate blade inplace at right angles to the blade shown in FIG. 2];

FIG. 23 is a perspective view of a cube tap form of connector;

FIG. 24 is an alternative perspective view of the cube tap of FIG. 23showing the opposite face of the tap;

FIG. 25 is a sectional view taken along the line 25-25 of FIG. 26showing two prong terminals exposed in their embedded positions in thetap;

FIG. 26 is a sectional view of the tap taken along the line 26-26 ofFIG. 25;

FIG. 27 is a perspective view of the contacts of the cube tap in thesame relative position as they occupy in the tap and with caps shown inphantom poised to enter the respective contact slots;

FIG. 28 is a perspective view of a form of contact formed to accomodatea power prong of round cross section;

FIG. 29 is a plan view of two such contacts positioned to receive a pairof power prongs;

FIG. 30 is an elevational view in part in section of the relation of acap and receptacle having contacts as shown in FIGS. 28 and 29;

FIG. 31 is a plan view of a contact blank prior to forming the contactcams;

FIG. 32 is a plan view of the contact such as is formed from a blank asshown in FIG. 31;

FIG. 33 is a vertical section of the contact as shown in FIG. 32 takenalong the line BB of FIG. 32;

FIG. 34 is a plan view of a contact having three cams;

FIG. 35 is a perspective view of a test connector structure;

FIG. 36 is a vertical sectional view of the structure of FIG. 35 takenalong the line A-A of FIG. 35.

Pursuant to the present invention contact structures may be provided inwhat may be indicated for convenience of reference as internally cammedstructures and as externally cammed structures. Internally cammedstructures are those formed with an essentially planar section ofmaterial surrounding a blade or prong receiving opening and having atleast one prong or blade gripping cam extending toward the blade orprong from the inner protion of the planar section. An internally cammedstructure is exemplified by that illustrated in FIG. 4.

The externally cammed structures are formed to have an essentiallyplanar section of material surrounding a prong receiving opening andhaving a prong gripping cam supported by said section from the outerportions thereof.

An externally cammed structure is exemplified by that illustrated inFIG. 17.

Reference will be made to these two distinct types in the descriptionwhich follows to add to the clarity of the description, but it will berealized that other forms of contact including combinstions of the aboveare within the scope of the present invention.

A description is given first in the text which follows of the internallycammed form of contact as this forms in unique in requiring the lowestmass of material of any contact known to provide a reliable andreproducible high contact pressure.

Referring first to FIG. 2, there is seen in this vertical sectionthrough the connector an alignment of the two internally cammed contactstrips and 22 in a single plane.

An important feature of the present invention is found in the ratherremarkable ability of the contacts to furnish power to a power receivingblade from a very thin plane of contacting material.

Still another feature which is complementary to that recited above isthe capability of internally cammed connector structures of the presentinvention to develop a high contact pressure on power receiving prongsor blades although the material of the contact strip of the connector isof thin gauge. Connector structures have been formed pursuant to thepresent invention from 70-30 brass of 0.016 inches thickness to providea double wipe action on a power blade. Moreover, the retaining force ofthis contact when properly embedded, as illustrated in the accompanyingfigures, in a yieldable material is higher than that of contacts whichemploy greater thickness of essentially the same metal in contact stripsof other constructions.

A connector formed in essentially the configuration shown in FIG. I,with a pair of contact strips each having a thickness of 0.016 inches aneach having a clearance between the opposed cams of fifty-fivethousandths of an inch, required a force of about 7.5 pounds to extracta pair of smooth surfaced brass power blades of a conventional cap fromthe grip of the corresponding pair of opposed cams in the connector. Inperforming this extraction force measurement, the cap blades were firstwithdrawn slightly, the withdrawal was interrupted and the measurementwas made as the withdrawal was again started to avoid in this way anyexcessive pull due to locking of the contacting insulating poritons ofthe cap and connector respectively.

A further remarkable feature of the connector of this invention is thatdue to the construction of the contact strip and the fact that it isembedded in the yieldable plastic, substantially less force is needed toinsert the power prong into the connector than is required to withdrawalit. In an insertion test essentially the converse of the extraction testdescribed above it was found that only 5.2 pounds of force was needed toresume the insertion of the same prongs starting from an at restposition, once the insertion had been initiated, into the same connectoropening which required the 7.5 pounds of extraction force referred toabove.

To continue now with an explanation of the advantages inherent in theplanar array of the internally cammed contacts of the present invention,it will be apparent by referring again to FIG. 2 that because the twocontacts lie in a single plane, it is feasible to employ a thirdcontact, which may also be of the planar configuration illustrated bythe dashed horizontal line 24 of the Figure, in close proximity to butinsulatedly separated from the two contacts 22 and 24. Similarly afourth contact 26, preferably also of planar formation, may be disposedin a plane slightly below but insulatedly separated from that containingthe coplanar contacts 20 and 22. The significance of this array ofcontacts is appreciated in connection with providing a grounding contactfor a connector such as that containing the two power contacts 20 and22.

To ensure maximum safety in use Underwriters Laboratories requires thatthe grounding prong or blade, of the conventional three prongedgrounding cap, contact the grounding contact of a connector before thepower prongs contact the power contacts of the connector.

Referring to the Figure it will be seen that a grounding prong insertedinto a cavity, such as cavity 28 shown in phantom in the body of theconnector, will provide a contact of the grounding prong with groundingcontact 24 before the power prongs can contact the power contacts 20 and22 because of the greater proximity of the grounding contact to theexternal surface of the connector body, i.e., the surface at which theprongs enter the cavities.

Referring now to FIG. 6, some characteristics of the contact structureimportant to its capability to perform with high efficiency as anelectrical contact will be described.

First it is noted that the contact surfaces 50 are confronting but arealso essentially parallel to each other. It is important to note thatthe parallelism is not simply between edges of the cams, i.e., a linearparallelism, but is a parallelism between essentially planar surfacesobtained in forming the cams. In other words, the portions of the camswhich are confronting and which will bear against a power blade insertedtherebetween might be described in an ideal configuration as planeparallel surfaces in that they are essentially planar surfaces which donot intersect.

Wide variation from the plane parallel configuration described above maybe tolerated without loss of the advantages of the present invention.However, the presentation of confronting edges which are so remote fromparallel planes as to constitute edges such as can bite into the powerblade surface are to be avoided in a contact structure prepared inaccordance with this invention.

An important feature of the internally cammed structures of the presentinvention may accordingly be seen to be the provision of, a high contactpressure and the provision ofa cammed structure which requires awithdrawal force to remove a power blade which is higher than the forceneeded to insert the same blade between the same pair of contactsurfaces.

Particularly it is important that this is accomplished with smoothsurfaced power blades and without appreciable biting" of the power bladesurface by any sharp edges of the contact which scrape or bite into thepower blade surface as the blade is withdrawn from the contact.

Accordingly, a particularly valuable feature of the article of thepresent invention is found in its capability to receive a power bladewith greater facility than it releases the same blade.

Specifically, when a power blade is urged against or inserted in thecontact structure of the present invention the action of the blade onthe structure is that of forcing the contacts in a direction in whichthey are disposed to move with minimum resistance, i.e., in thedirection in which the blade itself is urged. Because in theinternally-cammed structure the opposed cam springs are integral withthe leaf spring from which they are formed and are supported more at theouter longitudinal edges thereof that at the longitudinal center by theyieldable material in which they are embedded, the resuit is a tendencytoward forming a central longitudinal fold" of the plate which tends toseparate the contact- I ing surfaces 50 of the spring earns 52.

Accordingly, a feature of the internally cammed structure of the presentinvention may be seen to be that of supporting said spring cams at theirouter ends so that force applied to the tips tends to urge the cams inthe direction in which they are best able to be deflected by the forceapplied. Further, it will be seen that by supporting the spring cams inthe yieldable material the deflection thereof occurs also at leastpartly through deflection of the surrounding land of leaf spring fromwhich they are supported.

Accordingly, several advantages of the present invention are gained bysupporting the surrounding land portion of said leaf spring in which thecams are disposed to permit deflection of both the cams and the landthereof responsive to the tractive force applied to the cams by thepower blade.

Because of this capability of the land to cooperate with the yieldablematerial in which it is embedded it will be evident that substantialadvantage is gained where a land of leaf spring material is supported atits periphery in a yieldable material such as a vinyl chloridethermoplastic polymer and where spring cams are formed internally of andintegrally with the supported land.

Considering now the action of the contact cams as the power blade iswithdrawn from a connector having a cross section as shown in FIG. 2, itwill be seen that as the withdrawal of blades and 32 is started theupper surfaces of the planar section of the land surrounding the bladeswill be drawn into higher pressure contact with the yieldable insulatingmaterial 35 of the connector. Accordingly, some yielding of the plasticmaterial and some deflection of the land of the contact strip willoccur.

As will be evident from the form of the contact, withdrawal of th bladeswill result in a combination of compression of the yieldable materialbearing against upper surfaces of the land portions of the contact and adeflection of the material of the land, the net effect of which will beto increase the pressure exerted by the parallel gripping surfaces onopposite sides of blade 30. This increased pressure will be due to atendency of the contact to form a central longitudinal fold the converseof that described above in explaining the effect of inserting the powerblade into the contact.

While the internally cammed contact structure of the present inventionis seemingly simple in design it will be realized from the foregoingdescription and from the preceding explanation of the significantfactors on which its functioning depends that the contact strip of thisinvention will function as a power delivering contact to power receivingblades with the advantages inherent in the construction and at optimumefficiency only if a balance is maintained between the factors explainedto be important to the provision of these advantages.

Through careful balance of factors outlined above the internally cammedcontact structure of the present invention attains an unusually highlevel of use of the high tensile forces and the reciprocally opposinghigh compressive or gripping forces which can be generated within aplanar section of metal. However, this high level of use can be obtainedonly if the planar section is restrained from deflecting, buckling,folding, tearing or splitting as the tensile force is increased. For arelatively thin section of metal it is necessary to restrain themovement of the portions of the section out of the plane where portionsof the metal tend to undergo such movement as the tensile andcompressive forces within the section are increased.

However, in restraining this movement it is not intended that thedeflection be entirely eliminated or prevented. Some deflection can bebeneficial inasmuch as it can permit a very short cam, such as cam 52shown in FIG. 6, to itself deflect as part of the deflecting movement ofthe planar section of the strip and thereby to exert the strong pressureagainst the surfaces of a power blade without an excessive bending ordeflection of the cams themselves. Such excessive deflection couldresult in their being set or permanently bent to a substantial degreebeyond the limits of their original alignment and spacing.

The cams shown in FIG. 6 are enlarged in comparison to those shown inFIGS. 1 or 2 and are shown in proportions more representative of cams asthey would be employed than the smaller representation of FIGS. 1 and 2.In particular the cams as shown in FIG. 6 emphasize the fact that theholding or gripping power of the structures of the present invention donot depend on the pressing of a pointed or sharp edge into the surfaceof the gripped blade to restrain its withdrawal.

From the foregoing it will be evident that for optimum results it isnecessary to establish a balance of factors indicated herein to beimportant to the successful application of the present invention inwiring device technology.

An idea of which is optimum may be gained by considering the ratio ofthe mass of metal used in a contact strip providing three contactopenings which accommodate power blades of conventional dimensions tothat of other contacts serving a comparable function. The successfulbalancingof forces acting through the land between the embeddingmaterial and the short internal cam is, of course, essential tominimizing the amount of metal contained in the contact strip.

Further, an idea the optimization is also gained by comparing the easeof operation of the contact, i.e., the facility to the user of makingand breaking electrical connection combined with the firm gripping forceexerted on the power blade, with the ease of operation of othercomparable connectors known in the art. The greater ease of insertingthe power blades of a conventional cap as compared to the ease ofwithdrawal are particularly indicative of the achievement of thisoptimization.

As is pointed out above, one of the features of the power deliveringstructure of the present invention is its capability, although of suchsmall overall dimensions, to develop high pressure against the powerblade inserted into contact therewith. The capability of this structureto generate high contact pressure is the result partly of the fact thatthe structure in developing the high compression against the bladeutilizes principally the tensile property of the strip material tocontain and offset. the high compression.

The tensile property can be utilized because the contact or grippingsurface is integral with a cam and the cam is formed by forming metalout of the plane of a section of strip, the remainder of which sectionretains said essentially planar configuraton. The cam in pressing on thebroad faces of the blade delivers compressive forces to the blade and tothe longitudinal portions of the blade contiguous to the fixed ends ofthe cams, the lateral portions of the blade accordingly being placed intension.

In their preferred forms both the internally and externally cammedcontacts of this invention are adapted to receive a power blade throughan opening in a planar section of metal, the planar section essentiallysurrounding the opening through which the blade is to pass and theplanar section being subjected to tensile forces in the region thereofproximate theedges of the blade.

An essential feature of the contact of the present invention is that thegripping force, or the force tending to resist the withdrawal of thepower blade,' can be stored in large degree in portions of anessentially planar section of metal surrounding the blade receivingopening, proximate the portion of the opening which receives thenarrower faces of the blade.

The balance of a number of factors important to the success of theinternally cammed structure of the present invention may be more clearlydescribed and illustrated witth reference now to FIG. 7 which is anenlarged perspective view of a contact strip having the general form ofthose provided in accordance with this invention.

Two blade receiving openings 72 and 74 are shown in their relation tothe tips of illustrative power blades 76 and 78 poised for entry intothe openings.

The action of the power blades will be described with reference to thegeneral nature of their interaction with the contacts inasmuch as thecontacts are shown are formed from a metal of thin section and otherwisein a form suitable for use embedded in a polymeric material having theplastic or yielding properties similar to those of vinyl chloride.

A feature of the invention is the capability of forming an internallycammed contact structure of very low mass. The low mass contact isformed from stock or relatively thin initial cross section and asevident from the figures above by removal of a small amount of metalfrom the stock.

To form an internally cammed contact structure of minimum lateral crosssection from a strip of metal having spring metal characteristics themetal strip must itself be of both a minimum thickness which permitsdevelopment of the residual spring pressure needed to provide electricalcontact with the cam, and of a minimum width which accommodates theconventional blade thickness of about fifty-five thousandths of an inch.

Referring now particularly to FIG. 7, it will be appreciated that forcontacts of the general configurations shown in the figures somedeflection of the essentially planar section of the contact strip out ofthe plane will result from the insertion of the power blade, or from thespreading of the cams by some other application of pressure at therespective opposed pressure transmitting or gripping surfaces of thecams of the contact.

Where the contact is not formed to be embedded within a plastic materialas illustrated in FIGS. 1 and 2, but is to be held within a more rigidinsulating structure as a structure of a conventional type of thermosetpolymer, the gauge or thickness of the metal of the strip stock fromwhich the contact is formed is generally heavier than when thereinforcing effect of the more yieldable thermoplastic is employed. Thewidth of the strip need, be no greater than that employed in producingthe contact to be embedded except if externally supporting tabs shown inphantom in FIG. 7: are employed.

For either the heavier or lighter gauge contact spreading of thegripping surfaces will tend to produce a bowing or tendency toward afolding as mentioned above of the essentially planar section surroundingthe prong receiving opening. For the internally cammed contactparticularly, the insertion of a power prong can have the effect oftending to fold the strip contact, that is, to bring the ends of thecams of the strip further out of the plane of the strip in a directionopposite to the direction in which the portions of the strip remotefrom, but parallel to, the gripping surface of the cams are moved as thepower prongs are inserted in the contact. The tabs 90 are accordinglypositioned to accommodate the folding type of flexing of a contactstrip.

This deflection or flexing of the contact strip from the inside outproduces a very high contact pressure.

There is in effect a mechanical advantage employed in the structure ofthe present invention in utilizing the movement of the short beaminternal portion of a leaf spring section to apply a pressure, and inutilizing the movement of the long beam outer portions of the spring todevelop the pressure. The extent of pressure which is applied iscontrolled by controlling the relation of the degree of spring biasingand spring deflection to the yielding of the yieldable material.

Returning now to FIG. 7, as the blade 78, for example, approaches andenters opening 74 it comes into contact first with the wedge shaped camsurfaces 80.

These surfaces perform the usual function of locating the blade tip topress with essentially equal force against each cam and to facilitate inthis way passage of the blade through the opening.

The cams perform the function of transmitting to the longitudinal flatsections 82 the force acting on the cam surfaces 80.

In turn, the longitudinal flat sections transmit to the transverse flatsections 84 a portion of the force received from the cams.

The manner in which the tension develops in these flat sections 84,which in combination constitute a planar annulus,-and in which they willbe flexed depends on the nature of the material and the manner in whichit is held.

For example, where the material is a copper beryl- Iium alloy formed andthen hardened in the manner described in the copending application Ser.No. 546,273 filed Apr. 29, 1966 and assigned to the same assignee as theinstant application, the flexure will be lessened due to the greaterstiffness of the copper beryllium alloy material.

Further, where one planar section is contiguous to another, and the camsurfaces accommodate blades entering from opposite directions, theflexing of one planar section can balance with that of the other asillustrated by the contiguous transverse connecting sections 84 and 86of FIG. 7. Thus, the openings such as 72 and 74 having a length betweentransverse connecting sections of slightly over one quarter of an inch,sufficient to accommodate a power blade having a width of one quarter ofan inch, can be placed on centers in a contact strip of 0.36 inches. Thewidth of the transverse connecting strips connecting the openings can beas small as 0.08 inches and still give high efficiency performance.

This high efficiency is due in part to the fact that the transverseconnecting strip is subjected to tensile force from insertion of blades76 and 78 into the respective openings of the contact structure.

In forming the contact of the present invention, particularly theinternally cammed structures, care must be given to avoiding formingstructures which will result in the concentration of stress at locationsin the contact which could lead to permanent deformation of the metal ofthe finished contact when the contacts are eventually placed in use.

The manner in which this is conveniently accomplished in accordance withthis invention is illustrated in FIGS. 3 and 4.

Referring first to FIG. 3, a contact strip is first formed from a blankstrip of suitable metal, such as 70-30 brass of spring temper, bypunching out the pairs of openings 10. The edges defining the openingsare curved at locations where stress concentration might occur. For acontact strip having the dimensions described above, a radius ofcurvature of 0.03 inches serves very well to curve the ends of thegenerally oval shaped openings having a largest dimension of about 0.16inches, the width of such openings being about 0.06 inches. The edgesare also kept free of sharp corners or other configurations at whichstress might be concentrated. The high degree of utilization of themetal strip is evident from the combination of the small dimensions ofthe strip from which the contact is formed together with the smallamount of metal removed from the strip.

Referring next to FIGS. 3 and 8, a shear is formed at the midline 12between the pairs of openings to permit the metal to be bent to form twocams extending out of the plane in which the surrounding metal of thestrip is disposed.

Referring now to FIG. 8, there is illustrated a section through a sheetfrom which a contact strip is formed taken along a line, for example 88of FIG. 3; that is, viewing the strip section through a punched opening10 of FIG. 3, it will be seen that a sheared midline 12 is provided. Thelongitudinal portion 82 of the strip beyond the opening 10 isaccordingly seen in section.

Referring now to FIG. 9, the first step in the formation of the contactelements such as that illustrated in FIG. 7 is carried out by bendingthe internal cam ends formed by shearing at the midline 12 down throughan angle of approximately 90 from the original plane in which themidline 12 is disposed. The bending or forming of the metal of the camends is preferably accomplished to impart to the cross section of thecam a radius as is evident from the cross section of the cam as shown inthe Figure. The resson for formation of the radius in the cam is evidentfrom consideration of FIGS. 10 and 7 with regard to the surface of thecam which is presented to and bears against power blades brought intocontact therewith.

Referring now to FIG. 10 it is evident that the cam edges formed byshearing as seen in FIG. 8 and bent through 90 as seen in FIG. 9, arebent through an angle beyond the 90 imparting a further forming actionto the cams to add a further angle of bend to that shown in FIG. 9. Thesurface 94 for example is formed by bending the cam through a 45 anglealthough this need not be done with formation of a curvature in the bentsection. Whether the second forming is done to impart a curvature to theformed section or not, however, the

net result is a bending of the sheared surface of the cam edge throughan angle of more than sufficient to eliminate the possibility of any ofthe sharp cam edges resulting from the shearing being brought or pressedagainst the blade.

The relationship of the curved section 92 of the cam to be pressedagainst the blade to the straighter section 94 may be seen best byreference to FIGS. 7 and 10.

In preparing contacts. in accordance with this invention it will besufiicient if the metal is bent to an angle which will provide acam-like surface to receive the surfaces of an entering power blade andwhich will also permit the force received by the cam to be transmittedto the land of the surrounding metal strip to substantially increase thetensile forces in the portion of the land proximate the narrower facesor longitudinal edges of the power blade. The portion of the cam whichactually bears against the power blade should not be fiat as shown inFIG. 2, unless the cam edges are specifially formed so as to prevent anybiting of the cam into the blade surface. The more economical way toaccomplish this is to bend the sharp edges out of the way as taughtabove. By the land metal of the internally cammed structure of thisinvention is meant the metal of the original strip from which thecontact is formed, which remains essentially in the plane of theoriginal strip after the contact opening is formed, which surrounds thisopening, and which extends out from the cams to the extent ofcontributing to the containment or application of contacting or grippingforce through the cams onto a blade once a blade is inserted through thecontact opening.

Accordingly, the surface actually bearing on the blade may be rounded orformed with a plurality of angles and it may even be shaped specificallyto increase the pressure on a limited area of the blade surface.

What is submitted to be a desirable accomplishment of this invention isas explained more fully above the increase of force which is applicableto a blade surface as a gripping force operating through increasing thepressure and the accompanied frictional resistance on the blade as aneffort is made to withdraw it. What is distinct about the pressing ofthe holding surface of the cams against the blade surfaces pursuant tothis invention is that an increased force is applied over a sufficientlylarge area as to result in a sufficiently low pressure to avoid anappreciable indentation, removal or deformation of the metal of eitherthe blades or the contact. Accordingly, in forming the cams it is notnecessary to resort to the use of protuberances or the use of acombination of protuberance in the contact surface with a depression orhole in the blade surface. Accordingly, the main increase which mustresult pursuant to this invention at the contacting surfaces of the camsand blades, as a blade is withdrawn from the grip of a contact, is theincrease in the frictional engagement between the surfaces and,accordingly, of the force needed to make the surface slide relative toeach other.

While it is generally true that in a connector such as that illustratedin FIGS. 1 and 2, a part of the holding of the blade can be due to thefrictional engagement between the blade and that portion of the plasticmaterial 34 extending beyond the tips of the engaging surfaces 40 of thecontact, the increased frictional engagement will be due primarily tothe cam action.

How this is accomplished may be seen with reference again to FIG. 7. Ifthe land of contact opening 72 is supported at its longitudinal portionby integrally formed tabs 90, it will be evident that an asymmetricalgripping force will be applied to the surfaces of a power blade by theessentially parallel surfaces 92 of the cams 94 if the tabs are held bysupports of relatively more rigid material, such as the conventionalthermoset resins including phenolic resins or the like used inconventional wall mounted convenience outlets.

By an asymmetrical frictional gripping force is meant one which changesin value when the direction of movement of a frictionally engaged powerblade is reversed.

For such a construction the remaining portions of the lands 86 and 88 ofthe contact will serve to contain to a large extent the force appliedcentrally of the land and accordingly many of the advantages of theconstruction of contacts in accordance with this invention will bepreserved.

Additional modifications of the structure and additions thereto may bemade without departing from the spirit and scope of the presentinvention.

It will be evident that because of the relatively thin depth of thecontact of the present invention relative to the longitudinal axis ofthe power blade the construction of outlets of smaller depth may beaccomplished. For example at the present time the outer dimensions ofthe depth of insulating housing of wall mounted outlets are normallyexpected to run in the order of one inch or more. This depth ofinsulation housing accommodates a length of power blade inserted intothe outlet which is only approximately five-eighths of an inch.Employing the contact structure of the present invention, convenienceoutlets can be fashioned which permit the maximum depth of the outlet tobe determined by the necessity for the fully inserted blade to be housedin insulation which is integral with the outlet. Where the fullyinserted blades of a power receiving cap are permitted to extend beyondthe insulated housing of the outlet, the outer depth dimension of theinsulating housing for the outlet less than the depth of the fullyinserted blades is made feasible by the contact structure such as isprovided in accordance with the present invention.

While it might at first appear that the advantages made possible asdiscussed above would for some reason necessitate a sacrifice of someother properties of the outlet, the reverse is found to be the case.This latter suprising result obtains because each of the functions whichthe outlet is to perform is performed with equal or greater reliabilityand convenience then in structures available heretofore. Of particularsignificance is the capability of the device to resist the tendencyfound in contacts operating through spring pressure alone to develop afatigue in the spring action on which maintenance of contact with theinserted power blade depends. Because the contact structure of thepresent invention is capable of exerting greater holding force, i.e., aforce to resist withdrawal of an inserted smooth surfaced powerreceiving blade greater than the force needed to insert the blade, thecontact of the present invention does not depend for its holding of theblade only on the spring action such as is essential for other contacts.Accordingly it is not subject to the loss of holding ability due todevelopment of fatigue, or to a set or permanent bending of the fingersof the contact.

As explained above an externally cammed contact structure is analternative of the internally cammed contact of thin vertical sectionand we turn now to a description of the externally cammed structure.

Referring now to FIGS. 11 and 16, an alternative form of the contact ofthe present invention is formed from a strip such as 110 by firstremoving metal from the strip to form two stress relieving openings 108and by then shearing the midline 112 of the metal separating these twoopenings. The next step in formation of this alternative form of contactis illustrated in FIG. 12 and involves bending up the ends of the strip114 to form an acute angle preferably of the order of with thehorizontal. This is similar to the forming step given with relation toFIG. 9 above.

The next step involves bending the next inner portion of the strip edges116 to bring the end portions 114 through a further angle and to causethe edge 113 to be rotated through a total of more than a 90 angle andessentially bring it into an obtuse angle with respect to the horizontalmid plane of the strip. This forming step also corresponds generally tothat described with reference to FIG. 10 above.

The following step shown in FIG. 14 is a dual folding of the strip alongtwo longitudinally extending fold lines 118 to separate the centralopposed edges 111 formed along the central shear line 112, and to bringthe outer edges 114 closer together as shown in FIG. 14. The connectingend section 120 of the contact strip supports the two rotated camportions, i.e., the portions extending between the edges 111 and 114respectively of the strip as best seen in FIG. 17 form the tensile planeof the contact. The relation of the connecting portion of the originalstrip to that of the completed contact may be seen from a comparison ofthese portions in FIGS. 16 and 17. It is evident that the connectorportion 120 forms the vertical of a C-spring, the confronting contactsurfaces 119 forming the opposed jaws of the C configuration from whichspring pressure is applicable.

The space between the contact surfaces IE9 is adapted to receive a powerblade such that the contact surfaces will be pressed against oppositesides of the blade due to the spring action of the C springs at each endof the contact.

The disposition of contacts such as are described above in one form ofoutlet provided in accordance with this invention may be explained withreference now to FIGS. 18 and 19.

Referring now to FIG. 18, the cammed structure of FIGS. 15 and 16 isseen formed integrally with and at the ends of a contact strip 122. Thestrip includes the two end contact portions 124 and two wire locking camportions 126 similar to those described and claimed in copendingapplication Ser. No. 417,740 filed Dec. 11, I964 assigned to the sameassignee as the instant application. Between the two sets of contactsand wire locking cams is a break off tab 128 which may be removed so asto split the strip into two electrically separated pairs of wire lockingcams and cammed contacts.

The form in which the contact strip is shown is adapted for insertioninto a rigid plastic housing as conventionally used in enclosing aconvenience outlet for wall mounting.

Referring now specifically to FIG. 19, the two contact strips asdescribed with reference to FIG. 18 are shown in place in an insulatedhousing.

To assure the desired cam action the gripping edges 119 of the cams arefree to move in the direction of movement of a power blade entering thehousing and do not abut against the inner surfaces of the housingentrance 121.

The clearance between the gripping surfaces 119 is smaller than thewidth of the power blade inserted therebetween so that a spring,pressure from the C spring member described with reference to FIG. 15 isexerted on a power blade inserted between a pair of gripping surfaces119.

However, as the blade is urged out of the grip of the contact thestrength of the grip is increased by the follower movement of thegripping surfaces 119 as explained more fully above with reference tothe cam operation of the gripping cams.

It is evident that the plane in which the compressive gripping force isapplied in the blades is below the level at which tension is generatedin the cross member 120, referring to FIG. 15, and at which the tensionis generated in the cover 123 of the plastic housing of the outlet shownin FIG. 19. The tension in the housing cover is generated by thespreading force of the upper edges 111 of the cams in the internal seaton the underside of the housing cover 111.

Referring now particularly to FIGS. 20, 21 and 22 another modificationof the contact of the. present invention is shown.

In this modification the contact is adapted to receive a power blade ateither of two alignments, the two alignments being essentially at rightangles in a T formation.

Referring to FIG. 20, the contact is formed with two layers of metal,one disposed over the other so that a power blade passes through both asit makes contact at either level. In the illustration shown the twolayers are parts of a single strip of metal, the same strip also beingbent to provide a vertically extending terminal 130 to which a contactscrew or other similar wire connection may be mounted as through screwreceiving hole 132.

Both the blade receiving of the upper contact 134 and that of the lowercontact 136 are provided with the internally cammed contacts similar tothose described with reference to FIGS. 4, 5 and 6 above.

A major difference is the addition of enlarged noncammed openingsthrough which a blade may pass without application of a grippingcontact.

Thus the upper contact portion 134 is provided with opening 138 throughwhich a power blade, shown more clearly as blade 160 of FIG. 22, maypass without the application of a cammed gripping contact of the typedescribed with reference to FIG. 7. This blade is aligned as thevertical member of the T formation.

However, a blade which is inserted through contact portion 134 in theother permitted alignment, seen best as blade 150 in FIG. 21, does makecontact with the cams 140 extending from the inner edges of the uppercross member of the T-shaped opening. The cam 140 formed on the edge inwhich the vertical opening 138 ofthe T-form opening is located is splitso that cammed contact with a blade such as 150 of FIG. 21 is made oneach side of the opening 138.

The converse is true of the lower contact 136 in that a blade aligned as150 in FIG. 21 does not make the cammed contact with the blade but ablade aligned as in FIG. 22 does make cammed contact with the blade 160.

The two contacts 134 and 136 are shown separated by a distance which ischosen to show clearly the two layers and the relations between thecammed and uncammed openings and the blades inserted therein. However,it will be appreciated that the contacts need be separated by no morethan the distance needed to allow the flexing and camming action of thetwo superposed strip portions.

The two may be superposed in contact by shortening the connectingportion 135 or by forming the two portions from separate strips and thenby electrically connecting the two together.

Referring now specifically to FIGS. 23 through 27 an alternative use ofcontacts as described with reference FIGS. 3, 4, 5, and 6 is nowdescribed. The contacts are used in a cube tap shown in perspective inFIGS. 23 and 24 as having an insulating casing having two pairs ofopenings 182 and 184 on one side and a single pair 186 on the other.

The general configuration of the insulating casing is similar to thatseen in FIGS. 1 and 2 with the notable exception that the upper sectionof FIGS. 23 and 24 show the end of the insulation casing which enclosesthe inner portion of a pair of power blades 188 as being squared ratherthan tapered as is the end of the casing of FIG. 1 at which the wireenters.

The positioning of the contacts in the cube tap casing is seen best inthe two sectional views of FIGS. 25 and 26, FIG. 26 being a verticalsection taken along the line 26 26 of FIG. 25 and FIG. 25 being avertical section taken along the line 25 25 of FIG. 26.

The contacts 190 and 192 are essentially the same as those shown inFIGS. 4, 5 and 6 with the exception that the end, normally folded orcrimped as shown in FIG. 4 to grip a wire end, is not folded as they areused in the cube tap. Rather they are joined by rivets 194 or 196 to therespective inner portions of the blades 188 as shown.

The relationship of the blades and contacts and their positioningrelative to the caps of entering power blades is seen best in FIG. 27where details of the contacts are seen with the casing 180 removed. Asevident from earlier disclosure the two end contact slots 200 and 204 ofeach contact strip 190 is formed to receive power blades such as 201 and205 in the same orientation as illustrated by the positions in which thephantom caps 210 and 214 are shown.

Cap 212 approaches contact strip 190 from the opposite side to positionblade 203 in contact slot 202.

The foregoing illustrates another of numerous possible combinations inwhich the contact strip of the present invention can be utilized.

Referring now specifically to FIGS. 28 through 36 a form of contact istaught which operates according to the principles set forth above butwhich is particularly well suited for contacting power prongs ofgenerally round cross section.

Referring now first specifically to FIG. 28 a strip of metal which maybe brass of the type normally used in electrical contact structures isformed into a contact element by first punching out a figure x to havean enlarged square center 220 as seen best in FIG. 31 and four slots 224extending outward from the corners of the square 220. V

Following the punching of the x the inner tips of the cams 226 are bentdownward to an approximate form illustrated best in FIG. 9 and are thenbent further downward to the approximate form illustrated in FIG. 10.The plan view of a contact adapted to receive round prongs after it hasbeen formed in the manner described is illustrated in FIG. 32 by whichit may be seen that four cams 228 are presented to an entering powerreceiving prong of round cross section. The relation of the poised prong240 to the contact is best seen by reference again to FIG. 28. The cams238 make contact at a small area of a generally cylindrical prong suchas 240 but the contact is at a sufficiently high pressure that highpower can be passed between the prong 240 and contact cams 238.

The metal strip 242 in which the cammed contact is formed mayconveniently have the form of a contact strip. Thus for example it maybe bent at a mid-portion 244 to provide a vertical section having aterminal screw receiving slot 246 at the lower end thereof and ahorizontal portion 248 in which the cam is formed.

In FIG. 29 two such formed contact strips 242 are shown in side by siderelation. This positioning of the contacts permits the two spaced powerprongs of a power receiving cap to be used in connection with areceptacle in which such a pair of contacts 242 may be insulatedlymounted.

In FIG. 30 a housing for one such receptacle is shown in phantom as itwould house a pair of contacts 242 shown in solid lines. Therelationship of a descending pair of prongs 240 of cap 250 to receivepower from cams 238 of contacts 242 is readily evident from the Figure.The terminal screws 252 and associated wire clamps 254 cooperate toattach a conductor (not shown) entering an opening 256 in the insulatinghousing to supply electric power to the contact 242 of the receptacle.The contoured flange 258 of the insulating housing is used in theconventional manner in mounting the receptacle in an appropriate wall orother location.

Turning now to FIG. 35 a test apparatus is illustrated as it was used intesting and demonstrating the remarkable ability of the contact of thepresent invention to supply comparatively high levels of electric powerto receiving prongs of the round cross section as shown.

In this test apparatus two contact strips 260 similar to those shown inFIGS. 31 and 32 were mounted in an insulated test housing 262 of polymethyl methacrylate. The housing is formed of a lid 264 and base 266 andthe contact strips 260 are mounted therebetween in conforming recessesformed 268 formed in the upper surface of the base member 266.

As seen more clearly with reference to FIG. 36 which is a verticalsection taken along the line A A of FIG. 35, two prong receivingapertures in the cover member 264 are superposed over two openings 272of larger diameter formed in the base member 266. Also as seen best inFIG. 36 slight vertical motion of the cammed end of contact strip 260 isfeasible as the depth of the recess was approximately double thethickness of the strip disposed therein. The actual thickness of thestrip stock from which the contact was formed was in one case 0.016inches and the depth of recess was 0.030 inches.

The contact is held in place in recess 268 by rivet 274 but due in partto the comparative thinness of the strip stock the end of the strip inwhich the contact is formed is free to move or float in the cavityformed by the recess 268 and overlaying cover member. The cover 264 andbase 266 are held together by the screws 276.

Referring again to FIG. 36 the hole 272 which is oversize relative tothe prong diameter and to the diam eter of holes 270 must be largeenough to accommodate the cams 238 depending from the contact strip 260.Moreover it must be able to accommodate the cams when they are expressedunder the influence of the entering prong. The relation of prong 240 andearns 238 of contact strip 260 is seen best in the vertical sectionalview of FIG. 33 which is a vertical section of the contact end of strip260 taken along the section line B B of FIG. 32. It is evident from FIG.33 that as the cams 238 undergo the types of motion described above instating the principles of operation of contacts of this invention thatthey must have room to move and flex in order to obtain the sought forimproved electrical contact and gripping action.

It has been found for example in tests of the contact described withreference to the test apparatus of FIGS. 35 and 36 that a cap or plugsuch as 250 of FIG. 30 could be plugged into the test apparatus andunplugged fifty times where the contactor was energized with DC voltageat l25 volts and where the cap was connected to a load which required atleast 22.5 amperes of current to pass through the contacts at a voltageof 125 volts. When this fifty cycle connect and disconnect test wascompleted the contact was subjected to a heat rise test by measuring theheat rise of the strip between the rivet and the cammed contact while 15amperes of current at a voltage of C were passed through the contacttoan inserted plug. A 16 C temperature rise was measured in each contactstrip after four hours of conducting this level of electricity at anambient temperature of 25 C.

From the foregoing it is evident that an unusually effective electricalcontact is provided pursuant to this invention.

Obviously other forms of the contact may be made which provide camaction as explained above. One such contact is illustrated in FIG. 34and it will be noted that is is also useful in providing electricalcontact to power receiving prongs of generally round cross section. Suchcontact can also be made with a two cam contact but the three camscenter the prong or are centered by it. The cams 280 are formed much inthe same manner as previously described with reference to FIGS. 8, 9 and10. The outwardly extending slots 282 have rounded ends to minimizestress concentration.

When prongs of smaller dimensions are used it is feasible to bring thecams into closer proximity to a central point by performing a secondaryforming action on the strip to channel the metal of the contact stripalong a portion thereof representing an extension of the slots. Thisportion is illustrated by the dotted lines 225 extending outward fromthe slots 224 of FIG. 31. By depressing the metal between the dottedlines to form a channel of the metal aligned with the slots the twosides of the slot may be brought closer together. The channel formed bysuch depression can provide a spring like structure which spring canoperate to deliver yieldable spring pressure to a prong of smaller crosssection while preserving in essence the action of the cams in grippingan inserted power receiving prong of smaller cross section.

1. An electrical contact adapted to receive and frictionally engage aplurality of power blades, said cOntact comprising a generally planarland of metal at least partially surrounding each of a plurality ofblade receiving openings, said openings being partially defined by twoopposed cams extending at an acute angle out of the general plane ofsaid surrounding land, the direction of extension of a pair of cams outof the plane of a first land being opposite to that of an adjoining landof the same strip, and the edges of said opening subject to stress dueto deflection of said cams being shaped to reduce concentration of saidstress, and said land being supported to permit deflection thereofaccompanying deflection of said cams, the contacting surface of a bladedeflected cam lying generally in a plane which is approximately planeparallel to that defining the surface of the blade against which itbears.
 2. The electrical connector of claim 1 in which a plurality ofopenings are aligned with a plurality of blade receiving ports of aplastic housing at least two of which are disposed on opposite faces ofthe plastic housing.
 3. A cammed electrical contact said contactcomprising a land of conductive spring metal, a generally rectangularopening in said land, a tab of land metal extending from at least one ofthe longer sides of said opening, at least the major portion of said tabextending below the general plane of said land to form a cam, the endportion of said cam extending further below the plane of said land andhaving a reverse bend to point the edge of said cam away from saidopening, and said cam having a curved outer surface at said reversebend, said contact being supported at outer portions of said land in ahousing.
 4. The contact of claim 3 in which the edges of said openingsubject to stress due to deflection of said cam are rounded to reduceconcentration of said stress.
 5. The contact of claim 3 in which theland is part of a metal strip which includes a plurality of suchopenings.
 6. An electrical connector comprising, a cammed electricalcontact said contact comprising a land of conductive spring metal, agenerally rectangular opening in said land, a tab of land metalextending from at least one of the longer sides of said opening, atleast the major portion of said tab extending below the general plane ofsaid land to form a cam, the end portion of said cam extending furtherbelow the plane of said land and having a reverse bend to point the edgeof said cam away from said opening, and said cam having a curved outersurface at said reverse bend, said electrical contact being embedded ina yieldable insulating plastic housing, said housing having a bladereceiving port aligned for entry of a blade through said opening intocontact with said cam.
 7. An electrical connector comprising a cammedelectrical contact said contact comprising a land of conductive springmetal, a generally rectangular opening in said land, a tab of land metalextending from at least one of the longer sides of said opening, atleast the major portion of said tab extending below the general plane ofsaid land to form a cam, the end portion of said cam extending furtherbelow the plane of said land and having a reverse bend to point the edgeof said cam away from said opening, and said cam having a curved outersurface at said reverse bend, an insulating housing, said contact beingsupported at outer portions of said land in such insulating housing, anda port in the insulating housing communicating with said opening.